Apparatus for pulling crystals from molten compounds



Jan. 22, 1963 R. GREMMELMAIER 3,074,785

APPARATUS FOR PULLING CRYSTALS FROM MOLTEN COMPOUNDS Filed Aug. 22, 1956 3 Sheets-Sheet 1 Fig. 1

1963 R. GREMMELMAIER 3,074,785

APPARATUS FOR PULLING CRYSTALS FR M MOLTEN COMPOUNDS Filed Aug. 22, 1956 3 Sheets-Sheet 2 31 F ,f 32 I l P J 34 III F I II 1 1 m: 3m C I I ,1

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Jan. 22, 1963 R. GREMMELMAIER APPARATUS FOR PULLING CRYSTALS FROM MOLTEN COMPOUNDS 3 Sheets-Sheet 3 Filed Aug. 22, 1956 3,074,785 APPARATUS FOR PULLIWG CRYSTALS FRQM MOLTEN CGMPOUNDS Rolf Gremmelmaier, Erlangen, Germany, assignor to Siemens-Schuckertwerke Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Filed Aug. 22, 1956, Ser. No. 605,6il9 Claims priority, application Germany Aug. 26, 1955 14 Claims. (Cl. 23--273) This invention relates to apparatus for pulling crystals from a melt of a material, such as that used for the production of semiconductor monocrystalline crystals for electrical, photoelectrical or optical purposes, and more particularly to apparatus for producing crystals from materials which comprise highly volatile components.

Several methods have been proposed for such purposes, all of them having in common that the melt is produced and subjected to crystal pulling Within a sealed vessel under the application of two different temperatures to the vessel space, one temperature being applied at the melt proper and the other being applied in the environment of the melt within the sealed vessel. Such two-temperature crystal pulling methods are described in the copending applications Serial No. 45 6,249, filed September 15, 1954, now US. Patent 2,993,384, by H. Welker, O. Folberth, R. Gremmelmaier and R. Grimm, and Serial No. 534,- 852, filed September 16, 1955, by O. Folberth and R. Gremmelmaier. The terms substance comprising a high volatile component as used herein with reference to this invention, as well as with reference to the two-temperature methods of crystal pulling in general, is understood to include compounds such as stoichiometric and non-stoichiometric compounds, as well as alloys, which comprise one or more component elements whose partial vapor pressure above the melt, in the condition of equi librium, is considerably higher than the partial pressure of the other component or components and also higher than the partial pressure of any resulting compound of the components being processed.

The types of apparatus heretofore available for the purpose of carrying out the above-mentioned two-temperature methods of pulling crystals within a sealed atmosphere require much improvement. They are generally or often of limited reliability and are also difficult to maintain in good operating condition for extended periods of time. The reason for these difiiculties is the fact that it is necessary in the known equipment to mechanically transmit the pulling movement from the outside into the sealed vessel and to also pass and to seal electric leads through the vessel for measuring and regulating the various temperatures.

It is an object of this invention to obviate these difiiculties.

T this end there is provided a movable pulling plunger or piston within the sealed melting vessel, the plunger being operated by a magnetic field which is produced by a magnetic system located outside the vessel and longitudinally movable as Well as rotatable relative thereto. The magnetic field is produced preferably by a permanent magnet situated outside of the sealed vessel. The field acts upon a soft-iron core Which is inside the sealed vessel. Preferably, the iron core is mounted on the pulling plunger within the sealed vessel. The permanent magnet is connected with a driving or operating mechanism capable of moving the magnet system along the melting vessel and also of rotating it about the longitudinal axis of the vessel. In this manner it is possible to combine, without appreciable difiiculty, the translatory crystal pulling movement with a rotational movement of the piston often desired for crystal pulling purposes.

According to another feature of my invention, I pro- Patented Jan. 22, 1963 1 ice vide the apparatus with a thermal image body, or model body, which is located outside of the sealed melting vessel proper but is arranged in the vicinity of the crucible and within the same operational range of the same heating device that produces the melting temperature in the crucible. I further provide means for measuring the temperature of this dummy or substitute body as an indication of the actual crucible temperature, thus requiring no electrical or other leads to pass through the walls of the sealed melting vessel.

These and more specific features as well as the advantages of devices according to the invention will be apparent from the description of the preferred embodiment described below with reference to the drawing in which:

FIG. 1 is a schematic vertical cross section through a crystal pulling device;

FIG. 2 is a lateral view of the same device, showing in addition the operating mechanism for the crystal pulling plunger;

FIG. 3 is a cross section taken along the line III-III of FIG. 2; and 7 FIG. 4 is an enlarged view of part of the cross section shown in FIG. 3.

The same reference characters are used in all illustrations for the same components respectively.

The crystal pulling process is effected within a tubular vessel 1 of quartz. Located in the vessel is the crucible 2 which is mounted on a support 3, both consisting, for example, of graphite. Also disposed Within the vessel is the crystal pulling piston or plunger 4. Disposed in the upper portion of the plunger is an armature body 5 of soft iron fused into a quartz jacket 41, FIG. 4. An intermediate layer 6 of a quartz fibre mass (quartz wool) provides a firm seating of the soft-iron core 5 within the pulling plunger. Crucible 2 and plunger 4 are made of graphite because metals would be attacked, at the employed operating temperatures, by the vapors of the high-volatile components. The lower portion of the plunger 4 carries, fastened in a holder 40, the crystal seed or germ 7 which is shown to have coalesced with the initial portion 9 of a crystal being pulled out of the melt 8 contained in the crucible 2.

Because of the generally necessary high minimum temperatures, for example above 500 C., the soft-iron core 5 must have a correspondingly high Curie point. A Co-Fe alloy having a Curie point above 900 C. is suitable for this purpose.

The tubular quartz envelope or melting vessel 1 is provided with a hook 10 at its upper end to facilitate lifting the vessel out of the apparatus. The vessel 1 rests upon a supporting pipe 11 of quartz. For conducting the heating sequence in accordance with the above-mentioned two-temperature method, the apparatus is provided with four heating devices 12, 16, '17, 18. The heating device 12 serves for heating the crucible 2 and consists of a tubular high-frequency coil which, in operation, is traversed by cooling water and is energized by a suitable source of high-frequency current. In addition to the crucible 2, a graphite body 13 is located within the supporting tube 11 within the effective heating range of the high frequency induction heater 12. The mass of the graphite body 13 is so dimensioned that it is thermally similar to the graphite crucible 2, in order that the temperature of body 13 may serve as a measure of the temperature obtaining in the crucible and the melt. For that reason the body 13 is herein called the thermal image body or dummy or model body. The model'body is disposed within an atmosphere of protective gas which is supplied through a nipple 14. For determining and regulating the temperature of the melt, a thermo couple 15 is inserted into the model body 13. Instead of this temperature measuring and regulating device, any other suitable measuring means, such as any known radiation pyrometer, may be used. The heating devices 16, 17 and 18 form individual resistance furnaces serving to heat the other portions of the melting vessel 1. The resistance furnace 16 consists of slitted chromium-nickel tubing. The resistance elements 17 and 18 are wire coils supported by bodies of ceramic material. To facilitate visual observation of the crucible zone, the furnace 18 is mounted on a ceramic body of stepped shape. The current supply leads to the respective heating devices are schematically represented by arrows.

The pulling piston or plunger 4 is displaced lengthwise of vessel 1 and is rotated with the aid of permanent magnet 19 The magnet 19 is protected by a cooling water jacket 42 (FIG. 4) whose water inlet and outlet conduits are denoted by 26 (FIG. 1). Another thermo couple 21 is provided for determining the temperature of the upper portion ofthe melting vessel 1. A tube 22 of quartz and a lining of quartz wool 23 holds the melting vessel 1 firmly within the apparatus.

The actuating mechanism for the magnet 19 is shown in FIGS. 2 and 3. The lateral view presented in FIG. 2 illustrates the mechanism employed to move the permanent magnet 19 vertically, to effectuate the crystal pullingmovement. FIG. 3 shows the mechanism employed to rotate the pulling plunger. The permanent magnet 19 comprises two aligned pole portions firmly joined to each other by a ring-shaped yoke 31 which is fixed upon rotary drum or pulley 310. A V-belt drive 32 rotates the pulley 310 and therefore the permanent-magnet assembly. Pulleyv 310 is mounted on or in ring 33% carried by support 33. This motion is transmitted to the pulling plunger. The magnet assembly and the belt drive are'mounted on the support or carrier 33 (FIG. 2). The carrier 33 is moved vertically by means of a mechanism comprising a spur gear34 which meshes with a rack gear 359 on column 35 andcan be operated by hand through a shaft 36 ('FIG. 3). The gear 34 can also be turned, through the gears 379, 371, by means of Cardanic-shaft drive 37, at a desired, predetermined velocity of vertical displacing motion. .Shaft 37 is turned by schematically indicated motor 372. It will be recognized that the rotating and displacing mechanisms may be modified provided that they secure the desired rotational and displacing movement of the magnet system.

The quartz jacket into which the soft-iron core is fused, is denoted by 41 (FIG. 4) the cooling jacket for the magnet 19 being denoted by 42.

The apparatus illustrated in the drawings is presented only by way of example. Various modifications and variations are applicable, particularly with respect to the design of the individual components of the apparatus. The design and shape of the melting vessel, the crucible, theheating devices, and the magnetic devices for transmitting motion through the melting vessel, as well as the mechanisms for imparting translational and rotational motion to the plunger can be adapted to special operating and manufacturing conditions.

Apparatus built in accordance with this invention eliminates the difficulties occurring with motion-transmitting mechanisms which are mechanically connected with the pulling plunger and which require mechanical elements to pass through the walls of the melting vessel. In view of the minimum temperature required for the described process, which is about 500 C. in the melting vessel, and also because of the chemical activity of highly volatile components such as arsenic or phosphorus, at these temperatures mechanical connections through the vessel wall are complicated and difiicult to make and maintain.

The apparatus according to the invention is suitable for the pulling of crystals, particularly monocrystals, according to any of the above-mentioned two-temperature methods. Particularly suitable for operation with such apparatus are A B compounds, that is compounds of an element from the third group with an element from the fifth group of the periodic system. This includes, for example, indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP) or gallium phosphide (GaP). Also particularly suitable for processing in the apparatus are compounds which, aside from the abovementioned arsenic and phosphorus, contain as a highly volatile component such elements as selenium, sulphur, iodine, bromine or mercury.

Although the piston moving apparatus has been shown in the form best adapted to perform the process described in the prior applications referred to above, it can, with slight modification, be employed to carry out the crystal pulling process described in US. application Serial No. 489,176, filed February 18, 1955, by R. Emeis, now abandoned. In this event, the positions of the external heating coils 12 and 18 are modified to provide for the melting of only a restricted upper and central region of the material in the crucible, in conjunction with an internal heat radiative element having no external connection or only one such connection.

I claim:

1. Furnace apparatus for pulling a semiconductor crystal from a melt of a multicomponent material having a more volatile component and a less volatile component, in an atmosphere of the more volatile component, comprising a sealed quartz vessel for confining said atmosphere, a crucible for the material stationed in said vessel, said crucible having an opening, a crystal-pulling piston in said vessel and displaceable relative to said crucible opening, said piston being constrained to substantially straight line crystal pulling displacement, crucible heating means situated externally of said vessel, a structure providing a magnetic field, a quartz encase magnet armature structure in said vessel and operatively connected to said piston, the structure providing a magnetic field being located externally of said vessel, means for controlled gradual displacement of the vessel and the structure providing a magnetic field relative to each other for transmitting relative pulling displacement between said piston and crucible, the walls of the quartz vessel having no mechanical or electrical elements passing therethrough.

2. The invention defined in claim 1, including a model body having a mass thermally equivalent, in heating-up and in cooling-down, characteristics to that of said crucible, said model body being mounted externally of said vessel near said crucible and Within the heating range of said crucible heating means, and temperature sensing means positioned externally of said vessel and thermally joined with said model body.

3. Furnace apparatus for pulling a semiconductor crystal from a melt of a multicomponent material having a more voltaile and a less volatile component, in an atmosphere of the more volatile component, comprising a sealed quartz vessel for confining said atmosphere, at crucible for the material stationed in said vessel, said crucible having an opening, a crystal-pulling piston in said vessel and displaceable relative to said crucible opening, said piston being constrained to substantially straight line crystal pulling displacement, crucible heating means situated externally of said vessel, a structure providing a magnetic field, a quartz encased magnet armature structure in said vessel and operatively connected to said piston, the structure providing a magnetic field being located externally of said vessel, means for controlled gradual displacement of the vessel and the. structure providing a magnetic field relative to each other for transmitting relative pulling displacement between said piston and crucible, the walls of the quartz vessel having no mechanical or electrical elements passing therethrough, said external structure providing a magnetic field flux oriented transversely of the quartz vessel, the crystal pulling being longitudinal to said vessel, the said armature structure comprising a soft-magnetic material having a Curie point of above 500 C.

4. Apparatus for pulling a semiconductor crystal from a melt of a semiconductor material having a more volatile component and a less volatile component, in an atmosphere of the more volatile component, comprising a sealed vessel of elongated shape for confining said atmosphere, a crucible for the material stationed in said vessel, and having an opening, a crystal-pulling piston in said vessel and adjacent the opening, said piston being rotatable transversely of said vessel and being displaceable longitudinally thereof, crucible heating means about said crucible externally of said vessel, a drive mechanism including a structure external to said vessel and providing a magnetic field flux oriented transversely of the vessel, and a magnet armature structure in said vessel and operatively connected to said piston, said external structure being movable longintudinally and rotatable transversely relative to said vessel to transmit a controlled gradual pulling movement and a controlled gradual rotary movement to said piston, said drive mechanism including means operatively connected to said external structure to effect the longitudinal and rotary movement.

5. In apparatus according to claim 4, said drive mechanism including a ring structure positioned coaxially about said vessel, said structure recited as providing a magnetic field being mounted on said ring structure, a support on which said ring structure is journalled for rotation about said vessel, drive means for vertically shifting said support, and drive means for rotating said ring structure on said support.

6. Crystal pulling apparatus, comprising a sealed vessel of tubular shape mounted vertically, a crucible in said vessel, a crystal-pulling plunger vertically displaceable in said vessel above said crucible, a magnet armature forming part of said plunger and having transversely opposite magnetic poles, a magnet field structure in whose field said plunger is located, said field structure being disposed externally of said vessel and providing a magnetic field having opposite magnetic poles acting transversely of the vessel, a ring structure coaxially surrounding said vessel, said structure recited as providing a magnetic field being mounted on said ring structure, a support on which said ring structure is journalled for rotation about said vessel, drive means for gradually vertically shifting said support, and drive means for gradually rotating said ring structure on said support.

7. A furnace for pulling crystals from a melt of a material in a gaseous atmosphere, comprising an hermetical- 1y sealed vessel for containing said atmosphere, a crucible for the material in said vessel, heating means including means for melting at least part of the material in said crucible, said crucible having a mouth opening, means in the vessel for mounting a piece of the material opposite the mouth, said piece mounting means being movable in a direction toward and from the mouth, means for moving the mounting including a body of ferromagnetic material which is inside the vessel and is operatively connected with said piece mounting means and including dipole means outside the vessel adapted for the impressing upon said inside body of a transverse magnetic field, means for controlled gradual movement of said di-pole means longitudinally of said vessel to move the inside magnet and the piece mounting means lengthwise.

8. The invention defined in claim 7 in which said means outside the vessel for impressing a movable magnetic field is further defined as including elements which rotate the magnetic field about an axis disposed lengthwise of the sealed vessel.

9. The invention defined in claim 7 in which the heating means comprises electro-inductive heating and heat radiative elements exclusively.

10. The invention defined in claim 9, including a model body having a mass thermally equivalent, in heating-up and in cooling-down, characteristics to that of said crucible, said model body being mounted externally of said vessel near said crucible and within the heating range of said heating means, and temperature sensing means positioned externally of said vessel and thermally joined with said model body.

11. A furnace for pulling crystals from a melt of a material, comprising a sealed vessel, a crucible for the material in said vessel, heating means including means for melting at least part of the material in said crucible, said crucible having a mouth opening, means in the vessel for mounting a piece of the material opposite the mouth, said piece mounting means being movable in a direction toward and from the mouth, means for moving the mounting including a magnet which is inside the vessel and is operatively connected with said piece mounting means and including means outside the vessel adapted for the impressing upon said inside magnet of a magnetic field, means to gradually move the magnetic field lengthwise of said sealed vessel, to move the inside magnet and the piece mounting means lengthwise gradually, said means outside the vessel for impressing a magnetic field having magnet poles facing each other on opposite sides of said vessel, and said armature structure being mounted on said plunger and having an elongated horizontal cross section providing two end faces opposite said two poles respectively.

12. A furnace for pulling crystals from a melt of a material in a gas atmosphere, comprising a sealed vessel for confining said atmosphere, a crucible for the material in the vessel, heating means for melting at least part of the material in the crucible, said crucible having a mouth opening, crystal pulling means in the vessel opposite the mouth for pulling a crystal from the melt in the crucible, an internal magnetizable device in said vessel operatively connected with said crystal pulling means, an external magnet field applying means outside said vessel for impressing a magnetic field upon the internal magnetizable device, means for relatively displacing the magnetic field and the magnetizable device to displace the crystal pulling means and the crucible mouth relatively with respect to each other, to cfiect the crystal pulling.

13. A furnace for pulling crystals from a melt of a material in a gas atmosphere, comprising a hermetically sealed vessel for confining said atmosphere, a crucible for the material in the vessel, heating means for melting part of said material in the vessel, said heating means being energized exclusively externally of said sealed vessel, and a model body having a mass thermally equivalent, in heating-up and in cooling-down characteristics, to that, of said crucible, said model body being mounted externally of said vessel near said crucible and within the heating range of said heating means, and temperature sensing means positioned externally of said vessel and thermally joined with said model body.

14. Furnace apparatus for pulling a semiconductor crystal from a melt of a multicomponent material having a more volatile component and a less volatile component, in an atmosphere of} the more volatile component, com prising a sealed vessel for confining said atmosphere, a crucible for the material stationed in said vessel, said crucible having an opening, a crystal-pulling piston in said vessel and disp-laceable relative to said crucible opening, crucible heating means situated externally of said vessel, a di-pole structure providing a transverse magnetic field, and .a transversely elongated ferromagnetic armature structure in said vessel and operatively connected to said piston, the said di-pole structure being located externally of said vessel, the vessel and the structure providing a magnetic field being displ-aceable relative to each other for transmitting relative pulling displacement between said piston and crucible, the ferromagnetic armature structure being in a sealed casing protectin g it from the chemical action of the said more volatile component, the ferromagnetic material of the arma- 7 E 8 ture having low residual magnet-ism to provide a sub- 2,763,666 Mastagli Sept. 18, 1956 stantially non-permanent magnet. 2,768,914 Buehler Oct. 30, 1956 2,851,341 Weiss Sept. 9, 1959 References Cited in the file of this patent UNITED STATES PATENTS 5 OTHER REFERENCES 2 206 096 Hendrey June 25 1940 Bell Tel. Lab., Transistor Technology, vol. 1, p. 144,

2,743,200 Hannay Apr. 24, 1955 sfigtember 1952- v 7 2,747,971 Hem May 29, 1956 The Reactor Handbook, vol. 2, sec. 2, chapter 2.7,

2,750, 10 {Franke J e 12, 195 Fig. PP- 337*359, y 1955- 

1. FURNACE APPARATUS FOR PULING A SEMICONDUCTOR CRYSTAL FROM A MELT OF A MULTICOMPONENT MATERIAL HAVING A MORE VOLATILE COMPONENT AND A LESS VOLATILE COMPONENT, IN AN ATMOSPHERE OF THE MORE VOLATILE COMPONENT, COMPRISING A SEALED QUARTZ VESSEL FOR CONFINING SAID ATMOSPHERE, A CURCIBLE FOR THE MATERIAL STATIONED IN SAID VESSEL, SAID CURCIBLE HAVING AN OPENEING, A CRYSTAL-PULLING PISTON IN SAID VESSEL AND DISPLACED RELATIVE TO SAID CURICBLE OPENING, SAID PISTON BEING CONSTRAINED TO SUBSTANTIALLY STRAIGHT LINE CRYSTAL PULLING DISPLACEMENT, CURCIBLE HEATING MEANS SITUATED EXTERNALLY OF SAID VESSEL, A STRUCTURE PROVIDING A MAGNETIC FIELD, A QUARTZ ENCASE MAGNET ARMATURE STRUCTURE IN SAID VESSEL AND OPERATIVELY CONNECTED TO SAID PISTON, THE STRUCTURE PROVIDING A MAGNETIC FIELD BEING LOCATED EXTERNALLY OF SAID VESSEL, MEANS FOR CONTROLLED GRADUAL DISPLACEMENT OF THE VESSEL AND THE STRUCTURE PROVIDING A MAGNETIC FIELD RELATIVE TO EACH OTHER FOR FIG01 TRANSMITTING RELLATIVE PULLING DISPLACEMENT BETWEEN SAID PISTON AND CRUDIBLE, THE WALLS OF THE QUARTZ VESSEL HAVING NO MECHANICAL OR ELECTRICAL ELEMENTS PASSING THERETHROUGH. 